There are two components in this project and both are extended from our continuous commitment to the clinical investigation of viral hepatitis. One of these is an effort to respond to the increasing demand for a more precise measurement of relevant genomic information in any viral infection. The knowledge of the presence of specific viral genes will help in identifying the infectious agent. However, to assess the stage of a disease, to evaluate the efficacy of a treatment, to determine the value of a predictor in the progression of a disease and to monitor the patient's disease progression, a more precise and quantitative analysis of the specific gene would be required. This previous research-oriented question can now begin to be answered in routine clinical laboratories with the advanced technology of molecular biology, such as polymerase chain reaction (PCR), and sequencing and mapping of the restriction nuclease digested fragments. We initiated developmental research in molecular diagnostic technology to meet our clinical need for HBV, HCV, and HIV infection. Whenever possible, we would improve the basic PCR technique to become a semi-quantitative procedure. During the last 2 years, we were able to apply the same principles of using PCR as primary study tool for viral infection to several newly identified human hepatitis viruses or suspected hepatitis viruses such as HGV, TTV, and SENV. We found that these viruses were at least ten-fold more prevalent in the donor population than HCV or HBV and were clearly transmissible by blood transfusion; however,they had no discernable impact on post-transfusion hepatitis. We were involved in the discovery of HGV (hepatitis G virus), but subsequently found that although HGV RNA was identified in both recipients and paired donor sera, it was also found in non-transfused controls and did not correlate with liver function abnormalities. Hence, no causative role for HGV in post-transfusion hepatitis was found and HGV, like TTV and SENV, remain blood-transmitted infections with no established diseaes associations. Paradoxiucally, other invetsigators have shown that HGV has a protective role against coexistent HIV infection and this is being further explored.The other part of this project is related to viral discovery. We have maintained an effort to find other viral agents responsible for hepatitis cases of unknown etiology, so called non-A-E hepatitis. Due to great resource requirements, we conducted these projects with industry partners under CRADA. We divided responsibilities by concentrating our effort to confirming initial discovery and establishing clinical relevance. In the past few years, we also engaged in developing cloning techniques for rare event genes that might identify low copy infectious agents from patient sera or tissues. The techniques developed were unique and with the potential to be applied to a large number of specimens at the same time. An invention report has been filed with the NIH technology transfer office and is being considered for possible patent application. Effort devoted to this project was reduced significantly since the demonstration of lack of significant clinical relevance of most of these newly discovered agents.